It is widely recognized that the color appearance of a visual stimulus changes as an observer continues to view it and that there are large individual differences in the time course of these changes. However, the exposure duration of stimulus materials in clinical tests of color vision is rarely carefully controlled. The aims of the proposed research are to describe and analyze individual differences among normal, anomalous, and dichromatic observers in time-related anomaloscope adjustments and wavelength discrimination measures, and to relate these individual differences to adaptation characteristics of underlying receptor processes and opponent hue-coding systems. During the current project period a large number of observers are being screened with a set of standard color-vision tests, including an anomaloscope for which test-field exposures are controlled at either 0.5 or 5 sec. A subset of these observers is then being tested systematically on the anomaloscope with a range of exposure durations from 50 msec to 10 sec to isolate groups of individuals with characteristically different patterns of adaptation. Preliminary data indicate marked losses of discrimination for most observers as the exposure duration increases from 500 msec to 10 sec. For a large proportion of the anomalous observers and some normals discrimination also deteriorates at durations shorter than 500 msec. The rate of change in discrimination as a function of duration is seen to vary across observers.